Field of the Invention
The present invention relates to a magnetic carrier and a two-component developer for use in an image-forming method that has a step in which an electrostatic latent image (electrostatic image) is developed (visualized) by an electrophotographic method.
Description of the Related Art
Electrophotographic methods have in recent years been used in image-forming apparatuses such as copiers and printers. Image-forming apparatuses that use an electrophotographic method must be able to support the output of a variety of images, such as fine lines, small characters, photographs, and full-color images. In addition, higher image qualities, higher definitions, higher image output speeds, and longer continuous runs are also being required.
The magnetic carrier used in the two-component developers that satisfy these requirements have taken the form of light composite particles with a specific gravity approximately from 2.0 to 5.0 and have little ability to fracture the toner even at higher image output speeds and longer continuous runs.
In order, in particular, to achieve a higher image quality for full-color images, a magnetic carrier must exhibit an excellent charge-providing ability for small particle diameter toners.
Thus, it is important for a magnetic carrier that it imparts a uniform amount of charge to the toner, that it is resistant to changes in the amount of charge imparted to the toner even during long-term use, and that environmental fluctuations do not cause changes in the amount of charge imparted to the toner (small environmental differences). A magnetic carrier that exhibits these properties must also have an excellent durability. As an example of these carriers, Japanese Patent Application Laid-open No. 2006-337579 describes a magnetic carrier that has improved durability by light-weighting of the carrier.
With regard to art that improves the durability of magnetic carriers, Japanese Patent Application Laid-open No. H7-104522 describes a magnetic carrier that has a silicone resin coat layer containing, for example, a silane coupling agent, disposed on the surface of a magnetic core material particle. Japanese Patent Application Laid-open No. S62-121463 describes a magnetic carrier provided by treating the surface of a magnetic core material particle with a coupling agent and then coating with a silicone resin. Japanese Patent Application Laid-open No. H4-198946 describes a magnetic carrier provided by treating the surface of a magnetic core material particle with an aminosilane coupling agent and then applying a coat layer containing a resin having a functional group capable of reacting with the aminosilane coupling agent.
In addition, a lightweight composite particle is commonly obtained by constructing a magnetic carrier core from a magnetic body component and a resin component. However, variations in the tinge and variations in the image density due to changes in the environment from a low-humidity environment to a high-humidity environment are one problem that can be caused by the use of a resin component for the magnetic carrier core. This is thought to be caused by the moisture adsorbability of the resin component.
With regard to the art of restraining the amount of moisture adsorption by a magnetic carrier particle, Japanese Patent Application Laid-open No. 2001-075315, Japanese Patent Application Laid-open No. H9-127736, and Japanese Patent Application Laid-open No. 2009-139707 describe art in which the amount of moisture adsorption by the magnetic carrier particle is regulated or specified.
However, recent years have seen demands for additional improvements in the durability of the magnetic carrier. There have also been demands for magnetic carriers to exhibit a greater suppression of the variations in image density and tinge that are induced by environmental fluctuations.